1. Field
This invention is in the field of the preparation of farinaceous batter by treatment by aquaceous material using a stirrer within a stationary mixing chamber with the stirrer rotating and orbiting.
2. Prior Art
In the field of large scale food preparation and packing, one of the problem areas has been the preparation of Tempura style batter, which is used to coat certain food portions prior to their being deep fat fried. Such food portions include seafood pieces, onion and other vegetable pieces, and poultry parts. "Tempura batter," or "tempura," are the names used in the food preparation trade to describe a thick leavened batter that swells in volume during frying.
Present practice for mixing tempura batter has taken two main forms. A first form takes advantage of the fact that the dry mix formulation is available in fifty pound paper bags, which fixes the dry mix batch size as an integral multiple of fifty pounds. The mixer used may be either a ribbon/paddle blender with horizontal paddle shaft, or a multiple speed commercial mixer with a vertical rotating mixing shaft which orbits around a vertical center line while the shaft also rotates. A wire whip affixed to the shaft is usually used to blend the components. In practice, the mixer operator adds one or two bags of dry mix to the mixer, adds water by reading a meter or weighing the water on a scale, then operates the mixer for a prescribed length of time at one or more prescribed speeds. The batch of tempura is then manually transferred to the tempura applicator which coats the food products.
A tempura applicator is usually comprised of an endless open mesh wire conveyor belt with a product carrying run that dips into a pool of tempura batter, dwells there for a few seconds, then rises from the pool and discharges the product over a pulley equivalent into a deep fat fryer. A second upper conveyor belt has a lower run of the same wire belt which closely follows the product run of the lower belt, to force product pieces below the surface of the pool.
A second form of mixer consists of a continuous mixing tank with a rotating vertical paddle shaft concentric with the vertical center line of mixing tank, an associated dry mix hopper with screw conveyor means to add dry mix to the mixing tank, and a variable water metering device to add water to the mix. The mixing tank is located relative to the tempura batter applicator so that the operating level in the mixing tank is somewhat higher than that in the tempura applicator. An outlet at the bottom of the mixing tank is piped to a point above the operating level in the applicator so that gravity may cause batter to flow from the mixer to the applicator when operating levels are correct, but no reverse flow is possible.
In practice, the dry mix hopper is filled by emptying a number of fifty pound bags into it. The dry mix feed screw and the water metering device are set to deliver the mix proportions required and the machine is started. As the water and dry mix pass through the mixing tank, they are essentially blended. The addition of components continues as the level in the mixing tank rises. When the mixing tank reaches operating level, mixed batter starts to discharge into the tempura applicator due to the difference in operating levels. This discharge continues until the batter applicator is filled to operating level, at which time a level sensor in the applicator shuts off dry mix feed and water feed, and may shut off the mixer paddles too. Additional transfer to the applicator and mixing of additional batter is now governed by the level sensor in the applicator.
Both of these mixing methods include disadvantages that are a continual aggravation to the food processor. In the batch mixing method, the mixer operator is responsible for accurately weighing or metering each batch of water, and for accurately timing each mixing cycle. Thus the operator may err in at least two measurements for each batch, and possibly three measurements if two mixer speeds are required, as they usually are. The operator must also manaully transfer up to thirty-seven hundred pounds of water and mixed batter per hour. A further disadvantage of this method is that the mixing cycle starts with the dry mix and water not blended, so that mixing paddles pass through one component and then the other until some initial blending has taken place. This is the reason that two mixer speeds are usually used, a first slow speed for a period of time to blend, and then a higher speed for a time to fully mix.
These mixing periods may total or even exceed the allowable mixing time before the mix begins to degrade by losing gases. A last disadvantage of this batch mixing method is that the level of batter in the applicator varies drastically by the size of the mixed batch. The variation in applicator level affects the dwell time of product in the batter because product enters the batter on a downsloping belt and leaves the batter on an upsloping belt. Therefore, as the batter level in the applicator drops, the product enters the batter later and leaves sooner. Variation in dwell time results in variation in coating, especially when product pieces being coated are frozen as with fish portions.
The disadvantages of the continuous mixing method are less obvious. The dry mix feed accuracy is based upon the assumption that the dry mix will feed at a constant rate depending upon screw speed. In practice, the amount of dry mix in the dry mix hopper affects the compaction of the mix in the screw, so that a given screw speed will deliver more from a full hopper than from a nearly empty hopper. In addition, the moisture content of the dry mix also affects the compaction in the screw. The combination of these means that the screw may deliver either loosely or more densely compacted chunks of dry mix to the mixer, and that the rate of delivery is continually changing as the hopper level varies and as new bags of dry mix are added to the hopper. In turn, this means that the mixed batter transferred to the applicator is continually changing. A further disadvantage of the continual mixing system is that at the end of the shift, the mixing chamber is full of mixed batter, which is usually discarded because it cannot be transferred. Another disadvantage to continuous mixing of tempura is that the method is not adaptable when solid shortening must be mixed into the tempura. Solid shortening is virtually impossible to meter, and the mixing speeds used are too low to blend solid shortening into the batter. This method is less labor intensive than the first method, and also produces a nearly constant operating level in the applicator.
Tempura is a mixture of water, and dry solids in finely divided form, sometimes also containing liquid or solid shortening. The dry solids component is a formulation of wheat and/or corn flours, egg and/or milk solids, gums, spices and flavorings, and leavening. Usually the tempura is mixed in a ratio by weight of approximately one water to one dry mix, but a particular product may require more or less water.
At the present time, there are individual food processing lines in use which require the accurate mixing of 2,500 pounds per hour of tempura batter. If the batter is not accurately mixed, the final product will vary in appearance, weight and taste. The problem is further complicated because tempura is subject to some degradation after two minutes mixing, and degradation becomes increasingly severe after about three minutes. Degradation occurs because the leavening reacts with water to form small gas bubbles and prolonged agitation causes the gas bubbles to leave the tempura. Once the gas bubbles have been removed from the tempura batter, the batter will not swell as desired during frying. An associated complication is that if tempura is allowed to stand for long periods of time before use, very little agitation will remove all gases. This combination of required mixing accuracy, short mixing time and relatively short holding time means that tempura must be mixed quickly in relatively small quantities, and must then be used relatively quickly.
The present invention is a tempura batter mixer which eliminates all of the disadvantages of the previously discussed mixing methods, and incorporates all of the advantages, while having some features not available in either. A vertical mixing tank is fitted with a vertical shaft mixing cage which can rotate at an infinitely variable speed, and at the same time the entire mixing cage can orbit at an independently and infinitely variable speed' about the vertical center line of the mixing tank. A dry mix hopper is provided with a moving belt bottom so that dry mix can be fed to the mixing tank in non-compacted or fluffy state, at any speed desired. A water holding tank is provided, equipped with automatic filling, adjustable volume/weight control, and emptying means. Both the dry mix batch (of either 50 or 100 pounds) and the amount of water to mix it with can be delivered, by this invention, to the mixing pot in about thirty seconds. A low agitation transfer pump is provided, infinitely variable in speed, for moving mixed batter to the batter applicator on demand. Once controls are set, the operator is only responsible for filling the dry mix hopper and pushing one button.
It may be seen that one object of the invention is to eliminate operator error in water measure and mixing time. Another object is to ensure that dry mix and water are added to the mixer in a way that minimizes separation and speeds blending. Another object is to reduce mixing time to a bare minimum consistent with adequate mixing. Another object is to maintain batter applicator level nearly constant. An overriding object is to ensure that all batches are proportioned and mixed in the same way for the same time.